1. Field of the Invention
The present invention relates to an under-fill material and a method for producing a semiconductor device.
2. Description of the Related Art
As a first background, in recent years, demands for high-density mounting have been increased as electronic instruments have become smaller and thinner. Accordingly, for semiconductor packages, the surface mount type has become mainstream suitable for high-density mounting in place of the conventional pin insertion type. In the surface mount type, a lead is soldered directly to a printed board or the like. For a heating method, the whole of a package is heated by infrared reflow, vapor phase reflow, solder dip or the like to perform mounting.
After surface mounting, a sealing resin is filled in a space between a semiconductor element and a substrate for ensuring protection of the surface of the semiconductor element and connection reliability between the semiconductor element and the substrate. As this sealing resin, a liquid sealing resin is widely used, but it is difficult to adjust an injection position and an injection amount with the liquid sealing resin. Thus, there has been proposed a technique of filling a space between a semiconductor element and a substrate using a sheet-like sealing resin (JP-B1-4438973 and JP-B1-2833111).
Generally, for a process using a sheet-like sealing resin, such a procedure is employed that a sheet-like sealing resin is attached to a semiconductor wafer, the semiconductor wafer is then diced to form a semiconductor element, and a space between an adherend such as a substrate and the semiconductor element is filled with the sheet-like sealing resin integrated with the semiconductor element while connecting the semiconductor element to the adherend to perform mounting. In this process, a space between an adherend and a semiconductor element is easily filled.
As a second background, in mounting of a semiconductor element on an adherend, an electrode such as a solder bump provided on a semiconductor element is melted to electrically connect the semiconductor device and the adherend. At this time, for the purpose of removing an oxide film on the surface of the electrode, improving wettability of the solder, and so on, a flux agent derived from carboxylic acid or the like is added to a liquid sealing resin in some cases (JP-B1-3868179). Recently, there has been proposed a technique of adding a flux agent of carboxylic acid also to the sheet-like sealing resin as described above (U.S. Pat. No. 5,128,746).
As a third background, in the process described above, a space between an adherend and a semiconductor element is easily filled. On the other hand, as the circuit width and the distance between terminals in the semiconductor element are reduced, occurrence of even a slight displacement at the time of matching to a connection position during mounting may lead to damages of the semiconductor element, failures of joining during mounting, and so on, and hence to a reduction in yield ratio in production of a semiconductor device.
Concerning positioning during mounting, since a sheet-like under-fill material is previously laminated on the semiconductor element, the under-fill material is required to have such a level of permeability that a mark for alignment, which is given to the semiconductor element, can be recognized at the time of alignment of the semiconductor element and a substrate during mounting of the semiconductor element. However, since the under-fill material generally contains an additive such as a silica filler for improving its properties, the permeability of the under-fill material may decrease, so that it becomes difficult to align the semiconductor element and the substrate during mounting of the semiconductor element.
As an under-fill composition for solving the above-mentioned problems, there has been proposed a technique of improving the transparency of the under-fill material by combining a first curable transparent resin composition, which contains a colloidal silica dispersion and an epoxy resin, and a second curable flux composition which contains a curable flux composition (JP-W-2007-515524)).